Soap molding machines of the most common type presently on the market include an element called a disk or star or star-disk rotating on an axis set at right angle with respect to the direction of travel of the soap on feeder and discharge conveyor belts. This type of equipment, called "rotating disk machine", does not allow that a large number of molds be mounted because if the number of molds is increased, the disk diameter also increases and the resulting inertial forces cause severe mechanical and process problems. With such machines the production can be increased by increasing the speed while maintaining a constant number of molds and therefore they can be defined as "fast " type machines.
There is also another type of apparatus, less common, which includes an element, called a rotor, which rotates with a rotation axis parallel to the direction of travel of the soap on the feeder and discharge conveyor belts. Machines of this type, that could be called "rotor machines", allow a theoretically unlimited number of molds to be mounted along the major rotor axis; in practice, given the present state of the art, such machines are equipped with eight molds at the most mounted on one or two rotors. These machines can thus increase production by increasing the number of molds while operating at constant speed and they are therefore called "slow" type machines.
The machine speed in terms of strokes per minute is presently about 100-150 on the "fast " or disk type machines and 50-60 for the "slow" or "rotor" type machines, depending on the model.
Known molding machines, of the slow or rotor type, are subject to a series of disadvantages and problems. If 180.degree. rotor rotation is envisaged, it will be difficult to keep the molded piece on the rotor, since the high centrifugal force developed by the high rotor speed pulls the soap off the mold. Those types of equipments where the pieces to be shaped are delivered by means of arms mounting suction cups or other cumbersome feeder units, require a long displacement of the translating half-molds to allow enough space for the insertion of said feeder units; to travel the additional distance, the half-molds will also have to travel very quickly. In addition, feeder units increase manufacturing and operating costs.
In those machines where for each piece to be mold two half-molds are foreseen facing each other, at 180.degree. on the same rotor, there is a total of three half-molds for each piece to be molded: two for feeding and molding and one for discharging and cleaning. This increases operating costs of the molding machine.
The rotor carrying the half-molds must be cooled with an appropriate coolant. The use of a vacuum device to hold the soap in the rotational/translation phase is also normally required, as well as that of compressed air to expell it during the discharging phase. In those machines where the rotor always rotates in the same direction, fluid sealing problems will also arise.
From the Japanese publication No. JP-A-58 160 108 a molding machine for plastic material is known, in which the mold and countermold are capable of a rotating motion and a reciprocating linear motion.